An aqueous dispersion of polyurethane polymer has found extensive use in coating applications for its unique advantageous properties, including good adhesion to various substrates such as metal, plastics, and wood substrates, good wear resistance, elasticity and toughness and so on.
However, the polyurethane polymer has the disadvantages such as high cost, poor weatherability, poor water resistance, and poor alkali resistance. In order to improve the properties of the polyurethane polymer, it is usually modified with vinyl polymers, such as (meth)acrylic polymers. Conventionally, process for the modification comprises free radical polymerization of vinyl monomers with a urethane prepolymer containing ethylenically unsaturated functionality to form a urethane-vinyl hybrid polymer. Such kind of urethane-vinyl hybrid polymer combines the advantages of both polyurethane and vinyl polymers, and thus has an extensive prospect of application.
At present there is still a need for an improved urethane-vinyl hybrid polymer and as well an aqueous dispersion comprising particles of such hybrid polymer in the coating industry.